Orientation-selective 14N electron spin echo envelope modulation (ESEEM)

The determination of 14N quadrupole coupling tensor principal axis orientations in orientationally disordered solids

Heather L. Flanagan, Gary J. Gerfen, Albert Lai, David J. Singel

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30 Citations (Scopus)

Abstract

We present an orientation-selective ESEEM (electron spin echo envelope modulation) technique. From a measurement of the variation of the amplitudes of modulation components at 14N pure quadrupole frequencies as a function of irradiation position within an EPR (electron paramagnetic resonance) powder pattern, we determine the orientation of the principal axes of the quadrupole coupling tensor relative to the principal axes of the tensor which governs the dispersion of the EPR spectrum in an orientationally disordered sample. The pure quadrupole frequencies appear when the EPR frequency is selected such that the nuclear Zeeman and the hyperfine interaction are approximately equal in magnitude. We have applied the method to a mercaptoethanol complex of myoglobin in which the pure quadrupole frequencies originate from 14N in the proximal imidazole ring. Our results enable us to validate the assignment of the quadrupole modulations to the metal-coordinated nitrogen of the imidazole ring, to correlate the principal axes with the principal values of the quadrupole coupling tensor, and to determine the orientation of the imidazole ring relative to the principal axes of the (low-spin) Fe(III) g matrix. These findings are discussed and compared with results of previous studies.

Original languageEnglish (US)
Pages (from-to)2162-2168
Number of pages7
JournalJournal of Chemical Physics
Volume88
Issue number4
StatePublished - 1988
Externally publishedYes

Fingerprint

electron spin
Tensors
Paramagnetic resonance
echoes
envelopes
quadrupoles
Modulation
tensors
modulation
Electrons
imidazoles
electron paramagnetic resonance
Mercaptoethanol
Myoglobin
Powders
rings
Nitrogen
Metals
Irradiation
myoglobin

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

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title = "Orientation-selective 14N electron spin echo envelope modulation (ESEEM): The determination of 14N quadrupole coupling tensor principal axis orientations in orientationally disordered solids",
abstract = "We present an orientation-selective ESEEM (electron spin echo envelope modulation) technique. From a measurement of the variation of the amplitudes of modulation components at 14N pure quadrupole frequencies as a function of irradiation position within an EPR (electron paramagnetic resonance) powder pattern, we determine the orientation of the principal axes of the quadrupole coupling tensor relative to the principal axes of the tensor which governs the dispersion of the EPR spectrum in an orientationally disordered sample. The pure quadrupole frequencies appear when the EPR frequency is selected such that the nuclear Zeeman and the hyperfine interaction are approximately equal in magnitude. We have applied the method to a mercaptoethanol complex of myoglobin in which the pure quadrupole frequencies originate from 14N in the proximal imidazole ring. Our results enable us to validate the assignment of the quadrupole modulations to the metal-coordinated nitrogen of the imidazole ring, to correlate the principal axes with the principal values of the quadrupole coupling tensor, and to determine the orientation of the imidazole ring relative to the principal axes of the (low-spin) Fe(III) g matrix. These findings are discussed and compared with results of previous studies.",
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TY - JOUR

T1 - Orientation-selective 14N electron spin echo envelope modulation (ESEEM)

T2 - The determination of 14N quadrupole coupling tensor principal axis orientations in orientationally disordered solids

AU - Flanagan, Heather L.

AU - Gerfen, Gary J.

AU - Lai, Albert

AU - Singel, David J.

PY - 1988

Y1 - 1988

N2 - We present an orientation-selective ESEEM (electron spin echo envelope modulation) technique. From a measurement of the variation of the amplitudes of modulation components at 14N pure quadrupole frequencies as a function of irradiation position within an EPR (electron paramagnetic resonance) powder pattern, we determine the orientation of the principal axes of the quadrupole coupling tensor relative to the principal axes of the tensor which governs the dispersion of the EPR spectrum in an orientationally disordered sample. The pure quadrupole frequencies appear when the EPR frequency is selected such that the nuclear Zeeman and the hyperfine interaction are approximately equal in magnitude. We have applied the method to a mercaptoethanol complex of myoglobin in which the pure quadrupole frequencies originate from 14N in the proximal imidazole ring. Our results enable us to validate the assignment of the quadrupole modulations to the metal-coordinated nitrogen of the imidazole ring, to correlate the principal axes with the principal values of the quadrupole coupling tensor, and to determine the orientation of the imidazole ring relative to the principal axes of the (low-spin) Fe(III) g matrix. These findings are discussed and compared with results of previous studies.

AB - We present an orientation-selective ESEEM (electron spin echo envelope modulation) technique. From a measurement of the variation of the amplitudes of modulation components at 14N pure quadrupole frequencies as a function of irradiation position within an EPR (electron paramagnetic resonance) powder pattern, we determine the orientation of the principal axes of the quadrupole coupling tensor relative to the principal axes of the tensor which governs the dispersion of the EPR spectrum in an orientationally disordered sample. The pure quadrupole frequencies appear when the EPR frequency is selected such that the nuclear Zeeman and the hyperfine interaction are approximately equal in magnitude. We have applied the method to a mercaptoethanol complex of myoglobin in which the pure quadrupole frequencies originate from 14N in the proximal imidazole ring. Our results enable us to validate the assignment of the quadrupole modulations to the metal-coordinated nitrogen of the imidazole ring, to correlate the principal axes with the principal values of the quadrupole coupling tensor, and to determine the orientation of the imidazole ring relative to the principal axes of the (low-spin) Fe(III) g matrix. These findings are discussed and compared with results of previous studies.

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VL - 88

SP - 2162

EP - 2168

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

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